Force Spectroscopy with a Novel Small Focus AFM

Atomic force microscopy has become potent tool for investigating interand intramolecular interactions. Single molecule force spectroscopy on supramolecular guest-host-complexes reveal information about the depth of the binding pocket and thermal off-rates. Sensitivity and resolution are immanently conntected to the cantilever’s mechanical properties. The cantilever’s thermal noise induced by Brownian Motion of the surrounding medium is a fundamental limit of resolution. As the Nyquist Theorem is valid for the thermal white noise of a cantilever, reduction of the viscous damping by downsizing the cantilever’s dimensions is compulsory. Furthermore, the resonant frequency is increased which extends experimental bandwidth and thus enables high speed measurements. Unfortunately small cantilevers cannot be used with commercially available AFM, since the laserfocus is too large. We present results of single molecule force spectroscopy measurements on Calixarene-Ammonium-Complexes acquired with our homebuilt small focus AFM. As predicted, small cantilevers show favourable properties as increased resonant frequency and lower viscous damping.